What really IS the difference between baking soda and baking powder? They look the same!
The short answer...ACID!
Baking Soda is "sodium bicarbonate". It is a base that reacts with acid and creates CO2 (carbon dioxide) making your baked goods RISE!
Baking POWDER is "double acting" meaning, it too causes "rise", but over an extended period of time. It contains the same as soda - sodium bicarbonate and it has two other acids as well, which allow it to release that CO2 over time therefore, creating lift while baking because of the heat!
The first acid - monocalcium phosphate - only reacts in a WET batter.
The second acid will most likely be sodium acid pyrophosphate, if you have selected a brand that is aluminum-free. This acid does not begin to react until it is 1.) Wet and 2.) Hot.
So your batter has additional time to get all those nice fluffy bubbles, resulting in a lighter texture.